1. Field of the Invention
The present invention relates to an optical transmission device, an optical transmission method, and an recording medium storing an optical transmission program.
2. Description of the Related Art
With an expansion of a demand for broadband communication due to widespread use of the Internet, it has been demanded to transmit large-volume data over a long distance in the optical communication network. To this end, an optical transmission system, in which an optical transmission device employing the WDM (Wavelength Division Multiplex) technology is installed at each node of a network, is put to practical use.
In optical transmission devices employing the WDM technology, since a plurality of optical signals in different wavelengths are multiplexed and transmitted, on a single optical fiber cable, to an optical transmission device at the next node, it is possible to increase transmission capacity per optical fiber cable.
In addition, in optical transmission devices employing the WDM technology, since a gain adjustment technique for detecting attenuation (transmission loss) of a multiplexed optical signal caused during transmission between optical transmission devices and for correcting the level of the received optical signal is further employed, it is possible to prevent the received optical signal from degrading and to transmit large-volume data over a long distance.
Now, to describe gain adjustment, the above-described optical transmission device will be described formally using FIG. 13. FIG. 13 is a diagram for describing a conventional optical transmission device.
As shown in FIG. 13, the conventional optical transmission device is connected to a previous-node optical transmission device that is installed at the previous node of the optical transmission device, and to a next-node optical transmission device that is installed at the next node of the optical transmission device. In addition, the previous-node optical transmission device and the next-node optical transmission device are configured in a manner similar to that of the optical transmission device shown in FIG. 13.
A reception-side optical amplifier AR11 receives a multiplexed optical signal transmitted from the previous-node optical transmission device through a transmission path F01, automatically performs gain adjustment on the received optical signal, and sends the gain-adjusted optical signal to a wavelength demultiplexing section D11. Meanwhile, gain adjust will be described in detail later.
The wavelength demultiplexing section D11 demultiplexes the gain-adjusted optical signal received from the reception-side optical amplifier AR11, and sends the demultiplexed optical signals to an optical switch S11. More specifically, the wavelength demultiplexing section demultiplexes the supplied multiplexed optical signal for each wavelength. For example, in transmission of an optical signal using 40 C-band wavelengths, the wavelength demultiplexing section D11 demultiplexes an optical signal, into which 40 waves having 40 different kinds of wavelengths are multiplexed, to optical signals having 40 different kinds of wavelengths.
The optical switch S11 receives the demultiplexed optical signals output by the wavelength demultiplexing section D11 and receives optical signals from a client terminal that a wavelength converting section T12, which will be described later, has received. The optical switch is a matrix switch that performs switching of a path for transmission to a wavelength converting section T11, which will be described later, and performs switching of a path for transmission to a wavelength multiplexing section M11, which will be described later, on the basis of information for each of these received optical signals.
The wavelength converting section T11 converts the wavelength of the optical signals received through the optical switch S11, and sends the converted signals to a client terminal. In addition, the wavelength converting section T12 converts an optical signal in a broadband wavelength received from a client terminal into an optical signal in a narrowband wavelength. In addition, the wavelength converting section T11 and the wavelength converting section T12 include a laser diode.
The wavelength multiplexing section M11 multiplexes the optical signals received through the optical switch S11, and sends the multiplexed optical signal to a transmission-side optical amplifier AS11. For example, in transmission of an optical signal using 40 C-band wavelengths, the wavelength multiplexing section M11 multiplexes optical signals having 40 different kinds of wavelengths.
The transmission-side optical amplifier AS11 amplifies an optical level of the multiplexed optical signal received from the wavelength multiplexing section M11 to a necessary optical level, and transmits the amplified optical signal to the next-node optical transmission device through a transmission path F12.
In addition, opposite to the above-described path, a reception-side optical amplifier AR12 receives a multiplexed optical signal transmitted from the next-node optical transmission device through a transmission path F21, automatically performs gain adjustment on the received optical signal, and sends the gain-adjusted optical signal to a wavelength demultiplexing section D12.
The wavelength demultiplexing section D12 demultiplexes the gain-adjusted optical signal received from the reception-side optical amplifier AR12, and sends the demultiplexed optical signals to an optical switch S12.
The optical switch S12 receives the demultiplexed optical signals output by the wavelength demultiplexing section D12 and receives optical signals from a client terminal that a wavelength converting section T14, which will be described later, has received. The optical switch is a matrix switch that performs switching of a path for transmission to a wavelength converting section T13, which will be described later, and performs switching of a path for transmission to a wavelength multiplexing section M12, which will be described later, on the basis of information for each of these received optical signals.
The wavelength converting section T13 converts the wavelength of the optical signals received through the optical switch, and sends the converted signals to a client terminal. In addition, the wavelength converting section T14 converts an optical signal in a broadband wavelength received from a client terminal into an optical signal in a narrowband wavelength.
The wavelength multiplexing section M12 multiplexes the optical signals received through the optical switch S12, and sends the multiplexed optical signal to a transmission-side optical amplifier AS12.
The transmission-side optical amplifier AS12 amplifies an optical level of the multiplexed optical signal received from the wavelength multiplexing section M12 to a necessary optical level, and transmits the amplified optical signal to the previous-node optical transmission device through a transmission path F10.
In addition, an OSC unit OS12 (OSC: Optical Supervisory Channel) performs information exchange between the previous-node optical transmission device and the optical transmission device through an optical coupler C11 and an optical coupler C14. An OSC unit OS11 performs information exchange between the optical transmission device and the next-node optical transmission device through an optical coupler C12 and an optical coupler C13.
An optical transmission device having such a configuration performs automatic setting of gain adjustment at the time of construction of a new optical communication network, installment of an optical transmission device at a new node, and addition of a part of an optical transmission device.
More specifically, at the time of booting of the previous-node optical transmission device, an adjustment optical signal is transmitted from the previous-node optical transmission device to the reception-side optical amplifier AR11. For example, the previous-node optical transmission device transmits a wave output from a laser diode, included in a wavelength converting section (corresponding to the wavelength converting section T12 shown in FIG. 13) implemented in the previous-node optical transmission device, to the reception-side optical amplifier AR11 as an adjustment optical signal. The reception-side optical amplifier AR11 detects an optical level of the adjustment optical signal received from the transmission path F01, and detects a transmission loss on the basis of an amount of attenuation calculated from the optical level.
By means of this, the reception-side optical amplifier AR11 automatically performs setting of gain adjustment necessary for amplifying an optical level of an optical signal received from the previous-node optical transmission device thereafter with reference to the transmission loss of the detected adjustment optical signal.
In addition, Japanese Unexamined Patent Application Publication No. 2004-23437 discloses a method for automatically performing gain adjustment in a reception optical amplifier at the next node by outputting ASE (Amplified Spontaneous Emission) light of a transmission-side optical amplifier as an adjustment optical signal. For example, ASE light output from the transmission-side optical amplifier AS11 shown in FIG. 13 is transmitted to the reception-side optical amplifier of the next-node optical transmission device through the transmission path F12. The reception-side optical amplifier detects the optical level of the received ASE light to detect a transmission loss on the basis of an amount of attenuation calculated from the optical level.
Meanwhile, the above-described conventional optical transmission device has a problem that a cost for equipment investment is high when short-and-intermediate-distance optical signal transmission is performed.